Eddy currents are induced in conductors in the presence
of changing magnetic fields. One of the first observations of eddy currents
was made by Bachhoffner of London in 1837 in his design for an induction
coil. He found that the coil was more effective when the solid iron core
was replaced by a group of iron wires insulated from each other. All subsequent
induction coil designs in the 19th century followed this practice.

Waltenhofen's Pendulum was made by Max Kohl of Chemnitz
and cost 50 Marks in the 1900 catalogue. The pendulum blade made of solid
copper would quickly come to rest in the magnetic field; the alternate
blade, with slots to break up the eddy currents, swings for a longer period
of time. This piece of apparatus is at Washington and Jefferson College.

Eddy currents produce heat, and this is demonstrated by
Foucault's Disk ,
in which a solid copper disk rotated in a magnetic field heats up.

I often use a Unipolar
Generator to demonstrate eddy currents. Bringing a large radar
magnet close to the freely spinning disk slows it down rapidly.

This pair of eddy-current pendula are about 1 m in height,
and swing between the poles of a radar magnet. They are in one of the physics
lecture hall preparation rooms at the University of Texas in Austin.